Stabilization of amido acids with antioxidants

ABSTRACT

The invention relates to stabilized amido acid compositions. More particularly, the invention relates to compositions of amido acids, such as 6-nonanoylamidohexanoic acid, stabilized with antioxidants. The stabilized amido acid compositions are useful in the manufacture of bleach activators such as sodium nonanamidohexanoyloxybenzenesulfonate. Bleach activators made from the stabilized amido acids of the invention are capable of possessing improved coloration.

This application claims priority under 35 USC 120 to and is a divisionof U.S. application Ser. No. 09/870,995 filed Jun. 1, 2000, now U.S.Pat. No. 6,660,712, and priority under 35 USC 119(e) to U.S. Provisionalapplication 60/208,502, filed Jun. 2, 2000, which are incorporatedherein by reference.

FIELD OF THE INVENTION

The invention relates to stabilized amido acid compositions. Moreparticularly, the invention relates to compositions of amido acids, suchas 6-nonanoylamidohexanoic acid, stabilized with antioxidants. Thestabilized amido acid compositions are useful in the manufacture ofbleach activators such as sodium nonanamidohexanoyloxybenzenesulfonate.Stablization of the amido acid protects chemical degradation.Additionally, bleach activators made from the stabilized amido acids ofthe invention possess improved color.

BACKGROUND

Hypochlorite and hydrogen peroxide are well known for their bleachingproperties. As a bleaching agent in laundry detergents, hydrogenperoxide has the advantage of being safe to use with many fabric dyes.However, hydrogen peroxide bleaches are not effective at temperaturesbelow 50° C. This limits their use as most laundering is carried out attemperatures below about 40° C. For this reason, various peroxyacidswere developed as alternative bleaching agents for use in laundrydetergents. The peroxyacids were generally found to be effectivebleaching agents at the lower laundering temperatures. Because of theirchemical instability and potential safety hazards, however, peroxyacidsthemselves are generally unsuitable for storage and handling.

Bleach activators were developed to address storage and handlingconcerns associated with peroxyacids. Bleach activators have the abilityto hydrolyze under laundering conditions, effectively producingperoxyacids, even at lower temperatures, e.g. below 40° C. Byperhydrolyzing bleach molecules, bleach activators enhance the activity,and thus the cleaning ability, of a laundry detergent. Bleach activatorshave the further advantage of being stable when stored in solid form atroom temperature. These properties permit the use of bleach activatorsin a wide variety of laundry detergents and other cleaning formulations.

An important class of bleach activators is phenyl ester salts. Aneffective bleach activator, phenyl ester salts readily react with bleachto form the corresponding peroxyacid. Exemplary phenyl ester salts,which are used as bleach activators, and their preparation are describedin U.S. Pat. Nos. 4,634,551; 4,852,989; 5,391,780; 5,393,905; 5,393,901;5,414,099; 5,466,840; 5,523,434; 5,650,527; and 5,717,118; as well as inpublished PCT applications WO 94/18159, WO 95/07883, WO 96/16148, and WO99/09004. These U.S. patents and published PCT applications areincorporated herein in their entirety.

Bleach activating phenyl ester salts can be prepared in various ways.For example, sodium nonanamido-hexanoyloxybenzenesulfonate can beprepared by reacting a C₉ fatty acid, and caprolactam to form6-nonanoylamidohexanoic acid. Sodium p-hydroxy-benzenesulfonate andacetic anhydride are then reacted with the nonanoylamidohexanoic acid(an amido acid) in a solvent to form sodiumnonanamidohexanoyloxybenzenesulfonate. This reaction mechanism is shownbelow in equations 1A and 1B.

The major difficulty with such a reaction is the formation of unwantedcolored by-products. As such, the final product can possess acommercially undesirable non-white appearance. The formation of thesenon-white, colored by-products are believed to be due in large part tothe oxidation of the amido acid intermediate formed during the process.Such an oxidation process may be similar to the oxidation ofN-alkylamides, as described by Sager: M. V. Lock and B. F. Sager, J.Chem. Soc. (B), (1966), 690, B. F. Sager, J. Chem. Soc. (B), (1967),428, and B. F. Sager, J. Chem. Soc. (B), (1967), 1047. Oxidation of theamido acid intermediate causes the formation of unwanted color as wellas chemical degradation of the amido acid—both of which are undesirable.

The removal of unwanted colored by-products from the commercial phenylester salts is difficult and expensive. Indeed, current techniques forremoving color from phenyl ester salts, such as sodiumnonanamidohexanoyloxybenzenesulfonate, either fail to produce acolorless, commercially desirable, white product or require undue timeand/or expense. For example, one technique used in forming amido acidphenyl esters involves sparging an inert gas through the amido acidreaction system. See, for example, U.S. Pat. No. 5,414,099. Anothertechnique which has been described involves admixing a water-basedpurification system with an amido acid phenyl ester sulfonate reactionproduct to form a purification system and separating the purified phenylester salt from the purification system such that a percentage of thecolor forming impurities are removed. See, for example, published PCTApplication WO 99/09004.

Accordingly, there is a need in the art for a simple, cost-effectivemeans of forming precluding or lessening the formation of coloredby-products during the synthesis of phenyl ester salts.

SUMMARY OF THE INVENTION

The invention answers the problems connected with forming substantiallydiscoloration-free phenyl ester salts, which may be used as bleachactivators. More particularly, commercially acceptable amido acids foruse in the formation of bleach activating phenyl ester salts generallyappear white and do not contain discolored amido acid by-products. Byemploying white amido acid products in the preparation of phenyl estersalts, a commercially acceptable phenyl ester salt can be prepared.

The invention aids in the prevention of discoloration and chemicaldegradation by providing stabilized liquid amido acid compositions. Morespecifically, the invention provides a stabilized liquid amido acidcomposition which contain at least one amido acid and an antioxidant.Additionally, the invention relates to processes of making a stabilizedamido acid composition as well as processes for preparing an amidophenyl ester salt from an antioxidant stabilized amido acid.

DETAILED DESCRIPTION

According to the invention, amido acids can be stabilized to prevent orreduce their discoloration and chemical degradation. These stabilizedamido acids are useful in the preparation of bleach activating, phenylester salts by processes known in the art. Simply put, the inventioncombines an antioxidant with an amido acid, typically a amido-carboxylicacid to form a stabilized amido acid. These stabilized amido acids maybe used in the preparation of bleach activating amido phenyl ester saltswhich may be used in laundry detergents, fabric softeners, hard surfacecleaners and other bleach-containing cleaning compositions.

Generally, discolored amido acid by-products and chemical degradationresult from the absorption of oxygen by an amido acid product. The amidoacid is particularly susceptible as a melt or in solution. To avoid theabsorption of oxygen into a liquid amido acid product, an effectivestabilizing amount of an antioxidant is added to an amido acid product.The presence of the antioxidant prevents or reduces the absorption ofthe oxygen such that the product does not become visibly discolored,e.g., a yellow or brownish coloration, or does not chemically degrade.

Amido Acids

The amido acids that can be stabilized through the use of the inventioninclude amido-carboxylic acids. Exemplary amido-carboxylic acids includethose represented by formulas I and II:

where R¹ is selected from C₁-C₂₂ alkyl, C₂-C₂₂ alkenyl, C₂-C₂₂ alkynyl,C₃-C₂₂cycloalkyl, and C₆-C₁₄ aryl; R² and R⁵ are each independentlyselected from hydrogen, C₁-C₂₂ alkyl, C₂-C₂₂ alkenyl, C₂-C₂₂ alkynyl,C₃-C₂₂ cycloalkyl, C₆-C₁₄ aryl, and where in formula II, R² and R⁵ cantogether with the nitrogen carrying them form a C₃-C₁₀ heterocycle; R³and R⁴ are each independently selected from hydrogen, C₁-C₁₀ alkyl,C₂-C₁₀ alkenyl, C₂-C₁₀ alkynyl, C₃-C₁₀ cycloalkyl, C₆-C₁₀ aryl and whereR³ and R⁴ may together with the carbon carrying them form a C₃-C₁₀cycloalkyl; and n is an integer from 0 to 20. The phrase “independentlyselected” means that the various radicals may or may not be the same.This phrase also means that when n is greater than 1, each CR³R⁴ groupmay or may not be the same.

Preferably, the individual substituents for the amido-carboxylic acidsof formulas I and II are as follows: R¹ is selected from C₅-C₁₅ alkyl,C₅-C₁₅ alkenyl, C₅-C₁₅ alkynyl, C₅-C₁₅ cycloalkyl, and C₆-C₁₄ aryl; R²and R⁵ are each independently selected from hydrogen, C₅-C₁₅ alkyl; R³and R⁴ are each independently selected from hydrogen, C₁-C₅ alkyl, C₂-C₅alkenyl, C₂-C₅ alkynyl, C₃-C₆ cycloalkyl, C₆-C₁₀ aryl and where R³ andR⁴ together with the carbon carrying them form a C₃-C₆ cycloalkyl; and nis an integer from 0 to 10.

More preferably the individual substituents for the amido-carboxylicacids of formulas I and II are as follows: R¹ is selected from C₇-C₁₁alkyl; R² and R⁵ are each independently selected from hydrogen andC₇-C₁₁ alkyl; R³ and R⁴ are each independently selected from hydrogenand C₁-C₅ alkyl n is an integer from 4 to 8. A particularly preferredamido acid is nonanamidohexanoic acid.

It is recognized that combinations of suitable, preferred and mostpreferred substituents can be used with the invention. For example, apreferred R¹ could be used in conjunction with a suitable R² and a mostpreferred R⁴.

Antioxidants

Any antioxidant or mixture of antioxidants capable of stabilizing theamido acids may be employed in the invention. Examples of preferredantioxidants include, but are not limited to, 1,3,5-trimethyl-2,4,6-tris(3,5-di-tert-butyl-4-hydroxybenzyl) benzene (sold under the product nameEthanox 330® from the Albemarle Corporation), Tetrakis(methylene(3,5-di-tert-butyl-4-hydroxyhydrocinnamate)) methane (sold under theproduct name Irganox® by Ciba-Geigy), butylated hydroxytoluene (BHT),and mixtures thereof.

An effective amount of an antioxidant for stabilizing the amido acid isany amount capable of preventing the oxidation of the amido acid.Preferably the antioxidant is present in an amount that will not affectthe preparation of a bleach activating phenyl ester salt or itsproperties. Typically, the antioxidant is present in the stabilizedamido acid composition in an amount of up to 5 wt %, more preferablyranging from about 0.001 to about 2 wt % of the composition, morepreferably about 0.01 to about 1 wt % and most preferably, about 0.01 toabout 0.1 wt %.

Stabilized Amido Acid Compositions

Typically, the amido acids of the invention do not undergo oxidationwhen the amido acids are in a solid state. Yet, when the amido acids arein solution and/or are a liquid or molten state, the amido acids canbecome oxidized resulting in the formation of visibly discolored amidoacid by-products. In contrast, the inventive stabilized amido acidcompositions are those that do not become visibly discolored when placedin a liquid or molten state. The amido acid discoloration is determinedunder normal lighting conditions by the naked eye.

Generally, the stabilized amido acid compositions are stable tooxidation discoloration and/or chemical degradation at a temperature ofabout 100° C. for approximately 70 minutes. Preferably, the stabilizedamido acid compositions do not become discolored when subjected toelevated temp for at least 120 minutes, more preferably 240 minutes andmost preferably 72 hours or more. To determine whether the amido acidcompositions are discolored, test samples of the amido acid compositionsmay be placed in tubes and then visually compared to colors of theplatinum-cobalt scale contained in an adjacent tube.

The stabilized amido acid compositions can be in the form of a solid(typically crystalline), a melt or dissolved in a solvent. Although thestabilized amido acid can be stored as a solid, the stabilized amidoacid is preferably stored as a liquid, e.g., a melt or a solution. Aliquid form is preferred because it can be easily pumped to a reactorfor conversion to a bleach activator. The use of solid, crystallinematerial is generally less preferred as the handling and continuousaddition of a solid to a reaction process is more difficult than aliquid.

Process for Preparing Stabilized Compositions

The stabilized amido acid compositions of the invention may be formed byadmixing the amido acids with an effective stabilizing amount of theantioxidant. The mixing of the two components may be accomplished by anyconventional means. It is understood, however, that it is preferred thatthe amido acid is not subjected to temperatures far exceeding itsmelting point prior to its admixture with the antioxidant.

One suitable process for preparing the stabilized amido acid compositionis to form a melt of the amido acid using a temperature slightly, 0-10°C., above the melting point of the amido acid. To this amido acid meltis admixed a stabilizing effective amount of the antioxidant. Anothersuitable process involves forming a solution of the amido acid, such asa solution of amido acid and sulfolane, and admixing the antioxidant tothe amido acid solution. Yet another process that may be used involvesforming a particulate or powdered mixture of the amido acid and admixingthe antioxidant to the powdered amido acid. This protects thecompositions from discoloration or degradation upon melting ordissolving. The process of preparing the stabilized amido acidcompositions may be performed either as a batch or continuous process.

Phenyl Ester Salts formed from the Stabilized Compositions

The stabilized amido acid compositions of the invention may be used toform bleach activating phenyl ester salts. The preparation of thesephenyl ester salts is discussed above. Phenyl ester salts prepared withthe stabilized amido acid compositions of the invention are preferablysubstantially free of amido acid discoloring by-products. Any bleachactivating phenyl ester salt that can be formed from an amido acid mayalso be prepared through the use of the inventive stabilized amidoacids.

Bleach Activated Compositions Containing Phenyl Ester Salts

The phenyl ester salts prepared from the stabilized amido acids of theinvention may be formulated into a wide variety of bleach activatedcompositions. Typically, the bleach activated phenyl ester salts of theinvention are employed in the formation of laundry detergents and hardsurface cleaners. Due to their ability to release hydrogen peroxide inan aqueous solution, however, the phenyl ester salts provide particularutility in laundry detergents for the bleaching of textiles. The bleachactivating phenyl ester salts may be formulated into a wide range ofdetergent compositions. Suitable detergent compositions for the phenylester salts of the invention are described in Bums et al., U.S. Pat. No.4,852,989, Bums et al., U.S. Pat. No. 4,634,551, Chapman et al., U.S.Pat. No. 5,534,194, Chapman et al., U.S. Pat. No. 5,534,195 and Guediraet al., WO 96/16148, herein incorporated by reference in their entirety.

The following examples are intended to illustrate, but not limit, thescope of the present invention.

EXAMPLES Example 1A Preparation of Recrystallized Amido Acid

Crude 6-nonanoylamidohexanoic acid (200.4 g) was fully dissolved in 300mL boiling methanol to give a brown solution and then cooled overnightin a refrigerator at approximately 0° C. The resulting cake was brokenup into a slurry that was filtered on a coarse glass frit and washedwith 100 mL room temperature methanol to give a white product and brownfiltrate and washings. 130.6 g amido acid was recovered from the glassfrit. The product was determined to have a melting point of 79.06° C. bydifferential scanning calorimetry (DSC) and a heat of fusion of 40.68cal/g.

Example 1B Preparation of Recrystallized Amido Acid

Amido acid (70.28 g) was recovered from the methanol filtrate andwashings of Example 1A by evaporation.

Example 1C Preparation of Recrystallized Amido Acid

Repeat the recrystallization of Example 1A with 200 g crude amido acid.

Example 1D Preparation of Recrystallized Amido Acid

Repeat the recrystallization of Example 1A with 150 g crude amido acidand 200 mL methanol. The solution was cooled to about 2° C. and theresulting solid was washed with about 30 mL −20° C. methanol. The yieldwas 119.06 g of white product.

Example 1E Preparation of Recrystallized Amido Acid

Repeat the recrystallization of Example 1A with 400 g crude amido acidand 500 mL methanol. The solution was cooled to about 2° C. and theresulting solid was sparsely washed with −20° C. methanol. The yield was278.76 g.

Example 2 Oxidation of Crystalline or Molten Amido Acid WithoutAntioxidant

Recrystallized amido acid (3.00 g) was placed in each of two 250 mLSchott bottles, each of which fit snugly in a GlassCol heating mantle.The temperature was held at either 80° C. (crystalline) or 100° C.(melt) for 24 hours using a Eurotherm/thermocouple assembly to maintainthe temperature. Oxygen absorption was measured using a MicroOxymax withone atmosphere of air. The oxygen consumption of various amido acidsamples was determined by the Micro-Oxymax (Columbus Instruments,Columbus, Ohio) which is a closed-circuit respirator used to measureminute amounts of oxygen consumed by a sample.

Strong oxygen absorption was observed for the melt, but negligibleabsorption was observed for the crystalline sample. The melt showed aninitial accelerating oxygen absorption. Specifically, at 14 hours anabsorption of 1800 uL was observed, at 23 hours an absorption of 3740 uLwas observed and at 26 hours an absorption of 4100 uL was observed.

Example 3 Oxidation of an Amido Acid Melt With or Without Antioxidant

Recrystallized amido acid (3.00 g) from Example 1D was placed in each oftwo 250 mL Schott bottles, each of which fit snugly in a GlassColheating mantle. To one of the bottles, 3.6 mg Ethanox 330, a highmolecular weight phenolic antioxidant (mw 774), was added beforeconnecting the apparatus to a MicroOxymax with one atmosphere of air.The temperature was held at 100° C. for 80 hours using aEurotherm/thermocouple assembly to maintain this temperature for bothbottles. At the end of the 80 hour test, the MicroOxymax detected about8250 uL oxygen absorption for the uninhibited sample and less than 250uL oxygen absorption for the Ethanox 330 sample. The Ethanox 330 amidoacid sample remained white, wherein the unstabilized amido acid sampleexhibited a strong brown color.

The experiment was repeated using 3.32 g recrystallized amido acid fromExample 1D and 6.1 mg Ethanox 330. The sample was placed in a glass bulbapparatus under 36.5 psig of pure oxygen. Holding the temperature at160° C. for 70 min. resulted in a brown melt.

Example 4 Oxidation of an Amido Acid Melt With or Without Antioxidant

Recrystallized amido acid (3.02 g) was placed in each of two 250 mLSchott bottles, each of which fit snugly in a GlassCol heating mantle.10.6 mg food grade BHT (2,6-di-tert-butyl-4-methylphenol) was added toone of the bottles and mixed on a steam table before connecting theapparatus to a MicroOxymax apparatus with one atmosphere of air. Thetemperature was held at 100° C. for 24 hours using aEurotherm/thermocouple assembly to maintain this temperature for bothbottles.

The uninhibited sample showed strong oxidation with the MicroOxymaxshowing approximately 9,100 uL oxygen absorption over 64 hours. TheBHT-inhibited sample, however, showed no oxidation.

Example 5 Oxidation of an Amido Acid Melt and a Methyl Ester MeltWithout Antioxidant

A methyl ester of the amido acid was synthesized by mixing 100.09 gamido acid from Example 1E with 150 mL methylene chloride and 47 mLthionyl chloride. The mixture was allowed to stand overnight. The nextday excess methylene chloride and thionyl chloride were removed byvacuum. A portion of the crude acid chloride (67.82 g) was treated with100 mL methanol with stirring at room temperature for two hours. Excessmethanol was removed by heating to 80° C. at 20 Torr. The product had anodor, possibly SO₂.

The oxidation experiment of Example 2 was repeated using two 3.0 g amidoacid samples from Example 1D. Oxidation was measured for either 30 hoursor 63 hours at 100° C. Strong oxidation of the amido acid was observed.

In contrast, two 3.0 g samples of the methyl ester of the amido acid wasmeasured for oxidation for 30 hours and at 63 hours at 100° C. Nooxidation was observed. The results of the MicroOxymax tests are shownbelow:

TABLE 1 Sample Time (hrs) Total O₂ uL Amido Acid 30 4858 Methyl Ester 3065 Amido Acid 63 9400 Methyl Ester 63 42

Example 6 Oxidation of an Amido Acid Melt Without Antioxidant

The experiment of Example 2 was repeated using 10.02 g amido acid.Oxidation was performed under about 35-41 psig of pure oxygen in a glassbulb apparatus, not a MicroOxymax. Oxidation was measured over 1786 min.A 5.6% decomposition of the amido acid occurred and a yellow/browncoloration of the amido acid product was observed.

The 5.6% decomposition was calculated as follows: 10.02 g amido acid wasplaced into the glass bulb. The glass bulb with the amido acid weighed86.4009 prior to testing and 86.3344 after having heated the bulb forthe 1786 minutes. Thus, there was a 66.5 mg oxygen weight gain(86.4009−86.334=0.0665 g=66.5 mg) in the amido acid which corresponds toabsorption of 2.08 mmole O₂. The 2.08 mmole O₂ represents a 5.6%conversion of the 36.92 mmoles of amido acid.

As depicted in Table 2 below, the data from the glass bulb test wasmeasured at ten different data points.

TABLE 2 Tank Bulb Pressure Data Point Time (Min.) Temp. (° C.) Temp. (°C.) Gauge 1 0 24.0 101.2 41.3 2 1 24.0 100.9 41.1 3 5 24.0 100.8 41.1 470 24.0 100.8 41.0 5 110 24.8 100.8 40.8 6 245 25.0 100.7 40.3 7 138624.5 101.0 35.9 8 1450 24.5 100.9 35.6 9 1615 24.0 100.6 35.3 10 178825.0 100.6 35.0

Example 7 Oxidation of an Amido Acid Melt Without Antioxidant

The experiment of Example 6 was repeated using 120° C. and 19.97 g amidoacid (mw 271) from Example 1A. Oxidation was measured at variousintervals over 250 min. A 4.8% decomposition of the amido acid occurredand a light brown coloration of the amido acid product was observed.

The 4.8% decomposition was calculated as follows: 19.97 g amido acid wasplaced into the glass bulb. The glass bulb with the amido acid weighed96.3984 prior to testing and 96.2846 after having heated the bulb forthe 250 minutes. Thus, there was a 113.8 mg oxygen weight gain the amidoacid, which corresponds to absorption of 3.56 mmole O₂. The 3.56 mmoleO₂ represents a 4.8% conversion of the 73.58 mmoles of amido acid.

As depicted in Table 3 below, the data from the glass bulb test wasmeasured at eleven different data points.

TABLE 3 Tank Bulb Pressure Data Point Time (Min.) Temp. (° C.) Temp. (°C.) Gauge 1 0 23 121.5 37.7 2 2 23 121.3 37.5 3 5 23 121.0 37.4 4 15 23121.0 37.1 5 55 23 121.0 35.4 6 80 23 121.0 34.0 7 110 23 121.0 32.5 8126 23 121.0 31.8 9 203 23 121.0 29.3 10 240 23 121.0 28.4 11 250 23121.0 28.0

Example 8 Oxidation of an Amido Acid Melt Without Antioxidant

The experiment of Example 7 was repeated using 20.12 g of nearly purewhite amido acid Oxidation was measured over 430 min. It was found that5.50 mmol of O₂ was absorbed with 7.42% decomposition of the amido acid.The amido acid had a light brown coloration.

The 7.42% decomposition was calculated as follows: 20.12 g amido acidwas placed into the glass bulb. The glass bulb with the amido acidweighed 96.6017 prior to testing and 96.4258 after having heated thebulb for the 430 minutes. Thus, there was a 175.9 mg oxygen weight gainin the amido acid, which corresponds to absorption of 5.50 mmole O₂. The5.50 mmole O₂ represents a 7.42% conversion of the amido acid.

As depicted in Table 4 below, the data from the glass bulb test wasmeasured at eleven different data points.

TABLE 4 Tank Bulb Pressure Data Point Time (Min.) Temp. (° C.) Temp. (°C.) Gauge 1 0 24.1 121.8 42.1 2 2 24.1 121.6 42.0 3 5 24.1 121.4 41.9 414 24.1 121.2 41.6 5 55 24.1 121.2 39.7 6 85 24.0 121.3 37.9 7 170 23.5121.1 33.4 8 276 23.0 121.4 30.5 9 330 23.5 121.2 29.5 10 375 23.1 121.228.7 11 430 23.1 121.1 28.0

Example 9 Oxidation of an Amido Acid Melt Without Antioxidant

The experiment of Example 2 was repeated using 10.01 g amido acid ofExample 1D, except the temperature was maintained at 100° C. for 2820min and also maintained at 120° C. for 3000 min. The amido acid meltreadily oxidized at the 100-120° C. temperatures 2.95 mmol O₂ wasabsorbed with a yellow/brown coloration observed. This oxygen absorptionwas calculated as follows: The weight of the bulb and amido acid priorto absorption was 86.43 g and after absorption the bulb and amido acidweight 86.3356 grams. Thus the amido acid absorbed 94.4 of oxygen whichis 2.95 mmol O₂.

As depicted in Table 5 below, the data from the glass bulb test at 100 °C. was measured at eleven different data points.

TABLE 5 Tank Bulb Pressure Data Point Time (Min.) Temp. (° C.) Temp. (°C.) Gauge 1 0 25.1 101.0 41.8 2 2 25.1 100.9 42.0 3 5 25.1 100.6 41.9 440 25.0 100.4 41.9 5 104 25.0 100.5 41.8 6 1320 25.0 100.8 38.8 7 141025.0 100.6 38.6 8 1750 25.0 100.4 38.3 9 1840 25.0 100.4 38.3 10 279023.8 100.9 37.5 11 2820 24.0 100.4 37.5

As depicted in Table 6 below, the data from the glass bulb test at 120°C. was measured at twelve different data points.

TABLE 6 Tank Bulb Pressure Data Point Time (Min.) Temp. (° C.) Temp. (°C.) Gauge 1 0 23.8 121.6 42.0 2 2 23.9 121.3 42.0 3 5 23.9 121.0 42.0 420 23.9 121.0 41.9 5 90 24.0 121.0 41.8 6 320 24.0 121.0 41.2 7 472 24.0121.0 41.0 8 1378 24.0 121.0 39.2 9 1800 24.3 121.0 38.8 10 1910 24.3121.0 38.6 11 2860 24.2 121.0 37.4 12 3000 24.2 121.0 37.5

Example 10 Oxidation of an Amido Acid in Sulfolane Without Antioxidant

Sulfolane (24.84 g) was placed in a 100 mL g lass bulb apparatus underabout 41 psig of pure oxygen. The temperature was maintained at 100° C.for 168 minutes and then raised to 120° C. and held there using aEurotherm/thermocouple assembly for an additional 142 minutes. 5.0 g (16wt %) amido acid from Example 1A was then added to the bulb and thetemperature maintained at 120° C. for 490 min. Slight yellow colorationof solution was observed.

As depicted in Table 7 below, the data from the glass bulb test at 100°C. was measured at six different data points. The oil bath temperaturefor the glass bulb was then raised to 120° C. and four more data pointswere taken.

TABLE 7 Tank Bulb Pressure Data Point Time (Min.) Temp. (° C.) Temp. (°C.) Gauge 1 0 23.0 99.7 41.2 2 2 23.0 99.6 41.0 3 5 23.0 99.7 41.0 4 3023.0 99.6 40.9 5 140 23.0 99.6 40.7 6 168 23.0 99.6 40.6 7 172 23.0122.6 42.0 8 190 23.0 120.7 42.1 9 210 23.0 120.6 42.0 10 310 23.0 120.841.8

As depicted in Table 8 below, once having added amido acid from Example1A, the data from the glass bulb test at 120° C. was measured at twelvedifferent data points.

TABLE 8 Tank Bulb Pressure Data Point Time (Min.) Temp. (° C.) Temp. (°C.) Gauge 1 0 22.5 120.8 41.2 2 2 22.5 120.7 41.0 3 5 22.5 120.7 40.9 420 22.5 120.7 40.8 5 50 22.8 120.5 40.6 6 130 22.8 120.5 40.3 7 185 22.8120.5 39.9 8 230 22.8 120.7 39.8 9 325 22.8 120.5 39.3 10 375 22.9 120.739.0 11 425 23.0 120.8 38.8 12 490 23.0 120.8 38.5

Example 11 Oxidation of an Amido Acid in Sulfolane Without Antioxidant

The experiment of Example 10 was repeated, except 20.02 (44 wt %) amidoacid from Example 1B was used. The amount of sulfolane, 25.29 g, wasapproximately the same as in Example 9. The 120° C. temperature wasmaintained for 445 min. 7.19 mmol O₂ was absorbed. It appeared thatthere was a rapid initial O₂ uptake, followed by rate decay.

The 7.19 mmol O₂ was calculated as follows: The bulb and amido acidweight 121.624 prior to oxygen absorption. After oxygen absorption thebulb and amido acid weight 121.6242. Thus, 230.1 mg O₂ absorption wasobserved which is 7.19 mmol O₂.

As depicted in Table 9 below, the data from the glass bulb test at 120°C. was measured at fourteen different data points.

TABLE 9 Tank Bulb Pressure Data Point Time (Min.) Temp. (° C.) Temp. (°C.) Gauge 1 0 24.2 122 42.7 2 2 24.2 121.8 42.5 3 5 24.2 121.6 42.2 4 2424.2 121.2 41.7 5 54 24.2 121.2 41.3 6 92 24.3 121.3 39.2 7 124 25.0121.2 36.8 8 150 24.5 121.2 35.0 9 178 24.5 121.3 33.0 10 220 24.5 121.330.4 11 300 25.5 121.0 26.5 12 344 24.5 121.2 24.9 13 396 24.8 121.023.0 14 445 25.0 121.3 21.7

Example 12 Oxidation of an Amido Acid in Sulfolane Without Antioxidant

The experiment of Example 11 was repeated, except 10.02 g (28 wt %)amido acid from Example 1D was used. The amount of sulfolane, 25.36 g,was approximately the same as in Example 9. The amido acid was added tosulfolane at 100° C. and maintained for about 1400 min. The temperaturewas then raised to 120° C. and maintained for an additional 180 min.There was negligible O₂ absorption over the 1580 min. period.

As depicted in Table 10 below, the data from the glass bulb test wasmeasured at fifteen different data points. The first ten data pointswere measure at the 100° C. temperature and the last four at the 120° C.temperature.

TABLE 10 Tank Bulb Pressure Data Point Time (Min.) Temp. (° C.) Temp. (°C.) Gauge 1 0 24.6 101.4 40.0 2 2 24.6 101.3 39.7 3 5 24.6 101.0 39.6 424 24.6 100.8 39.5 5 75 24.6 100.8 39.5 6 150 24.7 101.0 39.5 7 270 24.9101.2 39.5 8 346 25.0 101.0 39.4 9 402 25.0 101.1 39.3 10 1305 24.2101.8 38.5 11 1400 24.2 100.8 28.5 12 1410 24.5 120.8 39.8 13 1420 24.5119.9 39.7 14 1494 24.2 121.4 39.8 15 1580 24.2 121.4 39.8

Example 13 Oxidation of Methyl Ester of an Amido Acid WithoutAntioxidant

The methyl ester of an amido acid was prepared using 271.4 g of theamido acid of Example 1E mixed with 118.97 g thionyl chloride in 100 mLmethylene chloride. The solution was allowed to stand overnight. Thenext day 50 mL methanol was slowly added dropwise with stirring and thenallowed to stand. Some exotherm and boiling of the methylene chlorideoccurred. 25 g sodium hydroxide dissolved in 120 mL water was slowlyadded dropwise and there was some reflux of the methylene chloride. Themethylene chloride layer was then isolated using a separatory funnel,washed once with water, and dried with anhydrous sodium sulfate. Themethylene chloride was then removed using a rotovap.

46.24 g crude methyl ester product was obtained. 6.67 g was thenrecrystallized from 10 mL −10° C. methanol, and then washed with −70° C.methanol, yielding 4.78 g.

The methyl ester of an amido acid (206.7 mg) was placed in a 70 mL bulbat approximately 40 psi oxygen and held at 120° C. for 19 hours. Thebulb was then cooled and vented. The yellow product appeared to show aweight gain of 7.0 mg.

Example 14 Oxidation of Methyl Ester of an Amido Acid WithoutAntioxidant

The recrystallized methyl ester of an amido acid from Example 13 (3.0 g)was put in a 70 mL oxidation bulb at 120° C. 0.841 mmol O₂ was absorbedand there was much less than an 8.0% conversion. The yield of therecrystallized methyl ester was 16%. The product was a light yellowcolor.

As depicted in Table 11 below, the data from the glass bulb test wasmeasured at ten different data points.

TABLE 11 Data Time Tank Bulb Point (Min.) Temp. (° C.) Temp. (° C.)Pressure Gauge 1 0 24.0 121.0 35.5 2 2 24.0 120.8 35.5 3 5 24.0 120.635.4 4 30 24.0 120.4 35.1 5 73 24.0 120.5 34.9 6 100 24.0 120.5 34.6 7194 24.0 120.6 33.9 8 260 24.0 120.4 33.5 9 315 24.0 120.4 33.3 10 34524.0 120.5 33.1

Example 15

Oxidation of Crystalline Sodium Nonanamidohexanoyloxybenzenesulfonate at100° C. or 120° C. Without Antioxidant

2.50 g crystalline sodium nonanamidohexanoyloxybenzenesulfonate wasplaced in each of two Schott bottles. The temperature was held at 100°C. or 120° C. for 16 hours using a Eurotherm/thermocouple assembly tomaintain the temperature. Oxidation was measured using a MicroOxymaxwith one atmosphere of air. The crystalline amido acid gave slight O₂uptake and showed no discoloration at either temperature.

Example 16

Oxidation of Aqueous Sodium NonanamidohexanoyloxybenzenesulfonateWithout Antioxidant

A sample of sodium nonanamidohexanoyloxybenzenesulfonate recrystallizedfrom water (94 g) was dissolved in 20.41 g water and put in a 104 mLbulb. The solution was stirred with O₂ at approximately 120° C. for 312min. The solution showed a weight gain of about 7.5 mg.

As depicted in Table 12 below, the data from the glass bulb test wasmeasured at ten different data points.

TABLE 12 Data Time Tank Bulb Point (Min.) Temp. (° C.) Temp. (° C.)Pressure Gauge 1 0 23.0 121.7 54.0 2 2 23.0 121.4 57.0 3 5 23.0 121.258.0 4 10 23.0 120.9 58.2 5 40 23.0 121.0 57.3 6 134 23.0 121.8 56.8 7175 23.0 120.9 56.5 8 205 23.0 120.8 56.5 9 235 23.0 120.8 56.2 10 31223.0 121.0 55.5

Example 17 Oxidation of Aqueous SPS Without Antioxidant

Sodium phenol sulfonate (SPS) (10.13 g) was fully dissolved in 10.76 gwater. The solution was stirred with O₂ at approximately 120° C. for1200 min. The solution showed a weight loss of about 2.0 mg from watervapor loss. The product was a light yellow color.

The following table is a summary of the results of Examples 2-12 and14-17.

TABLE 13 Phase/ Temp Measuring Example Substrate Inhibitor Solvent TimeApparatus Results 2 Amido Acid — Crystalline  80° C. MicroOxymaxNegligible O₂ absorption. 24 hours Melt 100° C. Strong O₂ absorption bymelt. 24 hours 3 Amido Acid — Neat melt 100° C. MicroOxymax Usual O₂consumption by uninhibited 80 hours sample. 3.6 mg 100° C. Slightconsumption ofO₂ by inhibited Ethanox 80 hours sample; no discoloration.330 ® 4 Amido Acid — Neat melt 100° C. MicroOxymax Strong oxidation byuninhibited sample. 72 hours 0.35 wt % 100° C. No oxidation. BHT 72hours 5 Amido Acid — Neat melt 100° C. MicroOxymax Substantial O₂consumed. 63 hours Methyl Ester — Neat melt 100° C. MicroOxymax LittleO₂ consumed. of Amido 63 hours Acid 6 Amido Acid — Neat melt 100° C.Glass bulb, Moderate initial rate followed by rate 1786 min Pressuredrop decay. Conversion = 5.6% in 1786 apparatus minutes, yellow/brownproduct. 7 Amido Acid — Neat melt 120° C. Glass bulb, Strong O₂ uptake.4.8% conversion, and  250 min Pressure drop light brown product.apparatus 8 Amido Acid — Neat melt 120° C. Glass bulb, Rapid initial O₂uptake followed by rate  430 min Pressure drop decay. 7.4% conversionand light brown apparatus product. 9 Amido Acid — Neat melt 100° C.Glass bulb, Good initial rate of O₂ uptake with 2820 min Pressure dropsubsequent decay in O₂ uptake rate at each 120° C. apparatus temperature(autoretardation). Very low 3000 min RO₂H yield (0.5%). Yellow/brownproduct color. 10 16 wt % — Sulfolane 120° C. Glass bulb, Negligibleconsumption of O₂ Amido Acid Solvent  490 min Pressure drop apparatus 1144 wt % — Sulfolane 120° C. Glass bulb, Rapid initial O₂ uptake followedby rate Amido Acid Solvent  445 min Pressure drop decay. 9.7% conversionwith yellow apparatus product, high (44%) RO₂H yield. 12 28 wt % —Sulfolane 100° C. Glass bulb, No significant O₂ uptake at 100° C. orAmido Acid Solvent 0-1400 min Pressure drop 120° C. until addition of0.22% in t-Bu₂O₂ 120° C. apparatus (free radical initiator) at 12° C.,then rapid 1400-1580 oxidation. Very low RO₂H yield (3.4%). min 14Methyl Ester — Neat melt 120° C. Glass bulb, Conversion <8%, slightdecay in rate, of Amido  345 min Pressure drop very light yellow colorformation, RO₂H Acid apparatus yield = 16%. 15 Sodium — Crystalline 120°C. MicroOxymax No significant O₂ uptake. Nonanamido 16 hours Hexanoyloxy100° C. No significant O₂ uptake. benzene 16 hours sulfonate 16 33 wt %— Water 120° C. Glass bulb, Slight O₂ absorption and discolorationSodium  312 min Pressure drop Nonanamido apparatus hexanoyloxy benzene-sulfonate 17 50 wt % — Water 120° C. Glass bulb, Very small O₂ uptake.sodium 1200 min Pressure drop Phenol apparatus Sulfonate (SPS)

The claimed invention is:
 1. A process for preparing an amido phenylester salt comprising reacting in a reaction vessel the following: (i)an antioxidant-stabilized amido acid composition an effectivestabilizing amount of an antioxidant and an amido acid; and (ii) aphenyl alcohol salt, under conditions sufficient to form an amido phenylester salt, wherein the antioxidant-stabilized amido acid is of aformula I or II

where R¹ is selected from C₁-C₂₂ alkyl, C₂-C₂₂ alkenyl, C₂-C₂₂ alkynyl,C₃-C₂₂ cycloalkyl, and C₆-C₁₄ aryl; R² and R⁵ are each independentlyselected from hydrogen, C₁-C₂₂ alkyl, C₂-C₂₂ alkenyl, C₂-C₂₂ alkynyl,C₃-C₂₂ cycloalkyl, C₆-C₁₄ aryl, and where in formula II, R² and R⁵ canwith the nitrogen carrying them form a C₃-C₁₀ heterocycle; R³ and R⁴ areeach independently selected from hydrogen, C₁-C₁₀ alkyl, C₂-C₁₀ alkenyl,C₂-C₁₀ alkynyl, C₃-C₁₀ cycloalkyl, C₆-C₁₀ aryl and where R³ and R⁴ cantogether with the carbon carrying them form a C₃-C₁₀ cycloalkyl; and nis an integer from 0 to 20; and wherein the amido phenyl ester salt isof formula (III) or (IV):

where Y is selected from SO₃ ⁻M⁺, CO₂ ⁻M⁺, SO₄ ⁻M⁺, and N⁺(R⁶)₃X; M isselected from hydrogen, ammonium and alkali metal atom; R⁶ in eachinstance is a C₁-C₄ alkyl group; and, X is a halide, hydroxide,methylsulfate, or acetate ion.
 2. The process of claim 1, wherein theantioxidant-stabilized amido acid composition is in a liquid state, or aliquid melt state.
 3. The process of claim 1, wherein the amido acidcomposition contains an antioxidant selected from1,3,5-trimethyl-2,4,6-tris (3,5-di-tert-butyl-4-hydroxybenzyl) benzene,tetrakis(methylene (3,5-di-tert-butyl-4-hydroxyhydrocinnamate)) methaneand butylated hydroxytoluene (BHT).
 4. The process of claim 1, whereinthe stabilizing effective amount of antioxidant ranges from about 0.001to about 2% by weight.